1. Field of the Invention
The present invention relates to a surface texture measuring machine of an object and a method of correcting a measured value for the machine, and more particularly to a large surface texture measuring machine which can measure an object of a large size or a high precision surface texture measuring machine and a method of correcting a measured value for the machine.
2. Description of the Related Art
As well known in the art, a surface texture measuring machine, which measures the surface roughness, the waviness, the roundness, or the two- or three-dimensional shape of an object, comprises a vertical V-axis column of high rigidity, a vertically movable table, a horizontal X-axis guide, a slider, and a minute detector. The vertical V-axis column upstands from a base of the machine. The vertically movable table is supported to be vertically movable with respect to the V-axis column. The horizontal X-axis guide and the slider which is slidable along the X-axis guide are disposed on the vertically movable table. The minute detector is attached to the slider to be in contact with the surface of the object.
Recently, in order to meet the needs for processed products which are highly precisely processed, a large surface texture measuring machine which can measure an object of a large size or a high precision surface texture measuring machine is requested. In the case where a surface texture measuring machine is simply enlarged or made highly precise, when precision of measurement which is equal to or higher than that of a small surface texture measuring machine is to be obtained, there arises a problem in that the components, i.e., the V-axis column, the X-axis guide, and the slider must be sufficiently enhanced in rigidity.
In a large surface texture measuring machine which can measure an object of a large size or a high precision surface texture measuring machine, namely, increased section moduli of the V-axis column, the X-axis guide, and the slider that must not be deformed cause the weight of the whole machine to be very increased. As a result, it is difficult to obtain a practical measuring machine.
In view of the above-discussed problem of a large surface texture measuring machine or a high precision surface texture measuring machine, it is an object of the invention to provide a surface texture measuring machine which is small and light or has high precision of measurement although the machine can measure a large object, and a method of correcting a measured value for the machine.
In order to attain the object, the invention proposes a method of correcting a measured value for a surface texture measuring machine comprising: a column which upstands from a base of the machine; a vertically movable table which is supported to be vertically movable (movable in V-axis direction) with respect to the column; a V-axis detector which detects a vertical displacement amount of the vertically movable table with respect to the column; a horizontal X-axis guide which is disposed on the vertically movable table; a slider which is guided along the X-axis guide and which has a Z-axis detector that detects a surface texture of an object; and an X-axis detector which detects a horizontal displacement amount of the slider with respect to the X-axis guide. The method comprises: an error calculation step of calculating amounts of errors in X-axis and Z-axis directions at a reference position of the vertically movable table, the errors being due to deformation of the column, from a height from a basal portion of the column to the reference position of the vertically movable table, the height being obtained by the V-axis detector, and a horizontal displacement amount from a reference position of the X-axis guide to a position of a center of gravity of the slider, the horizontal displacement amount being obtained by the X-axis detector; and an error correction step of correcting a detection result of one or both of the X-axis detector and the Z-axis detector, in accordance with the amounts of errors obtained in the error calculation step.
According to the invention, the object can be attained also by a surface texture measuring machine comprising: a column which upstands from a base of the machine; a vertically movable table which is supported to be vertically movable with respect to the column; a V-axis detector which detects a vertical displacement amount of the vertically movable table with respect to the column; a horizontal X-axis guide which is disposed on the vertically movable table; a slider which is guided along the X-axis guide, and which has a Z-axis detector that detects a surface texture of an object; and an X-axis detector which detects a horizontal displacement amount of the slider with respect to the X-axis guide. The machine further comprises a control device including: a height calculating section for receiving an output of the V-axis detector, and for calculating a height from a basal portion of the column to a reference position of the vertically movable table; a horizontal displacement amount calculating section for receiving an output of the X-axis detector, and for calculating a horizontal displacement amount from a reference position of the X-axis guide to a position of a center of gravity of the slider; an error amount calculating section for receiving outputs of the height calculating section and the horizontal displacement amount calculating section, and for calculating an amount of an error in one or both of X-axis and Z-axis directions at the reference position of the vertically movable table, the error being due to deformation of the column; and an error amount correcting section for correcting a detection result of one or both of the X-axis detector and the Z-axis detector, in accordance with an output of the error amount calculating section.
In the above-mentioned surface texture measuring machine:
1) a feed screw and a ball nut that move the slider in the X-axis direction may be disposed on the vertically movable table, a piano wire piece in which both the ends are fixed to the slider in a state where the wire piece is directed in the X-axis direction may be added to the slider, and a tip end portion of a connection pin that is integrated with the ball nut may be fixed to the position of the center of gravity of the slider in the X direction; and
2) the machine may further comprise a temperature detector disposed in the vicinity of one or all of the X-axis detector, the Z-axis detector, and the object, and control device may further include: a temperature error coefficient calculating section for obtaining a temperature error coefficient from an output of the temperature detector and specific temperature characteristics of the X-axis detector, the Z-axis detector, or the object in which the temperature detector is disposed; and a temperature error correcting section for correcting the detection result of one or all of the X-axis detector, the Z-axis detector, and the object, in accordance with an output of the temperature error coefficient calculating section.